Polymer Immobilized Bimetallic Nanoparticle Catalysts for Selective Hydrogenation of Quinones and Integration of Quinone-hydrogenation and Its Derivatization Using Sequential and Continuous flow Systems

Several single metal and bimetallic nanoparticle catalysts immobilized on polymer supports have been developed for selective hydrogenation of quinones to hydroquinones. Au-Pt bimetallic nanoparticle catalyst showed the best reactivity and selectivity for this purpose. Though slight over-reduction proceeded under batch conditions, higher reactivity, selectivity, and robustness of the catalysts were confirmed under continuous-flow conditions with polydimethylsilane-supported catalysts. Various direct derivatizations of quinones, such as methylation, acetylation, trifluoromethanesulfonylation, and benzoylation were successfully performed under sequential-flow conditions to afford the desired products in good to excellent yields. Especially, air-sensitive hydroquinones, such as anthrahydroquinones and naphthohydroquinones, could be successfully generated and derivatized under closed sequential-flow conditions without decomposition. This sequential-flow systems showed various benefits of flow systems; suppression of over reactions by controlling residence time, facile use of unstable intermediates, continuous production and robustness of the system.